The invention relates to the field of semiconductor optoelectronic materials, and especially to a novel apparatus and method for bulk nitride single crystal growth with liquid phase epitaxy.
GaN is the third generation of semiconductor material, and due to its features such as broad band gap, high pressure resistance, and high thermal conductivity, GaN has a wide market prospect in the field of high-end GaN-based optoelectronic devices in manufacturing high power LEDs/Ds, high-frequency and high-speed microwave detectors, etc., which has attracted wide attention in the industry.
Since the GaN material is decomposed into gallium and nitrogen under normal pressure and at a temperature of 877° C., the melting of GaN can only be achieved at a high temperature and under high pressure (2220° C., 6 GPa). Free-standing GaN substrate is difficult to obtain using the traditional Czochralski method (also known as the vertical pulling method, Czochralski process, or CZ method) for preparing a single crystal semiconductor substrate such as silicon and gallium arsenide substrate. Deficiency of free-standing GaN substrate forces present. GaN-based devices to be manufactured by using heteroepitaxy technology. Lattice and thermal stress mismatches between the epitaxial material and the heterogeneous substrate lead to high dislocation density of the epitaxial layer, and affects performance of the device. Therefore, using homoepitaxy technology for developing a high-quality free-standing GaN substrate is the key to achieving high power LEDs/LDs and high-frequency and high-efficiency microwave power GaN-based devices.
Currently, the method for preparing bulk GaN crystal mainly includes hydride vapor phase epitaxy technology (HVPE), high temperature and high pressure method (HPNS), the Na Flux method, ammothermal growth method, and the like. HVPE has a fast growth rate and can produce a large-sized single crystal material, but the prepared GaN single crystal has problems such as high dislocation density (˜106 cm−2) and residual stress. GaN single crystal prepared by HPNS has good quality (˜102 cm−2) but rigorous growth conditions (1700° C., 2 GPa). A crystal synthesized by using the ammothermal growth method also has good quality (˜103 cm−2) but a slow crystal growth rate and high requirement of laboratory equipment, which is adverse to industrialized production. Moreover, Na Flux has moderate growth conditions (700-1000° C., 4-5 MPa) and good crystal quality (˜104 cm−2) and is currently the best way to prepare GaN bulk single crystal. Currently, Na Flux growing of GaN has made some progress, bulk GaN single crystal with a diameter larger than 2 inches and a thickness more than 2 cm has been obtained. However, the traditional autoclave generally has only one chamber for mixing the raw materials and the seed crystal together and then is directly heated for single crystal growth. As such, during the period of initial heating-pressurizing and later cooling process, the raw material solution inevitably contacts the surface of the seed crystal when the growth conditions for the single crystal are not met, forming a polycrystal GaN and other intermediate phase products and thus affecting the crystal quality of the material. At the same time, the GaN polycrystal is formed at the gas-liquid interface, which causes slow growth rate of the crystal and low utilization rate of raw materials, which is an insurmountable defect of the traditional single-chamber autoclave.